Compositions for removal and prevention of scale are well developed in the patent art. "Scale" is a term that applies to deposits on surfaces such as bath tubs, shower tiles, cooling towers, heat exchangers, evaporative coolers, swimming pools, fountains, hydraspas, water purification systems, and the like. Scale deposits usually include compounds such as metal carbonates, oxides, bicarbonates and hydroxides primarily of Ca, Mg, Fe which deposit on surfaces in contact with water generally as a result of exceeding the limit of solubility of such materials in water. A considerable number of patents have issued covering compositions for the removal or prevention of scale including U.S. Pat. Nos. 3,447,965; 3,490,741; 3,639,279; 3,671,448; 4,435,303; 4,595,517; 4,686,067; 4,797,220 and 4,802,990. These patents are not the only patents related to the subject matter of this invention and they are not represented to be the most pertinent prior art. They are merely illustrative of various descaling and scale prevention compositions that have been disclosed in prior patents.
Many formulations disclosed in the above mentioned patents are acidic or alkaline in nature and have many disadvantages, such as irritation to the skin, eyes and mucous membranes during use. Additionally, prior formulations tend to react with the surfaces with which they come into contact during use including metal, ceramic and grout surfaces. Other known compositions tend to rapidly generate carbon dioxide gas as a result of their reaction with metal carbonate during use. Another disadvantage of current compositions is their potential reactivity with chlorine-containing materials with which they may be used to generate chlorine gas during use or storage.
In particular, for example, U.S. Pat. No. 4,797,220 discloses an aqueous composition of hydroxyacetic acid and triethanolamine at volume percentages of 0.7 to 10 of the acid to the amine with a 2 to 3.5 ratio being preferred. These compositions are highly acidic with pHs on the order of about 2-3 and can attack various metal surfaces, dissolve tile grout, react with chlorine-containing cleaners and irritate mucous membranes. While other alkaline compositions have been suggested, they suffer from similar disadvantages and are generally less effective.
In brief, there has been a continuing need for effective chemical compositions and processes for removal and prevention of scale. There is a need for compositions that would minimize or eliminate the disadvantages associated with known compositions.